BROOKLYN’S Monica Bailey, the candy store manager who nearly won “Big Brother 2,” has some advice for her “Big Brother 3” cousins: The “Big Brother” competition is a marathon – and these kids have been sprinting.

“They’re doing too many things too quickly in the game – I was in that house damn-near 80 days and they’re burning out too quickly,” Bailey told The Post.

There have already been several sets of alliances made – and broken – not to mention romances. And the show is only in its third week.

“They’re giving the public too much too quickly. They’re thinking too far ahead – the outcome in this game is going to change from day to day,” Bailey says.

Bailey, who came in third on last summer’s “BB2” behind Will and Nicole, said the “BB3” roommates seems to be pairing off fairly early – including Chiara and Roddy and Eric and Lisa.

“I have a feeling this group will have sex” too, she said, alluding to houseguest Chiara Berti, who shared versions of her sex life on national TV Wednesday night.

“Chiara is not talking about smearing honey on her body for nothing.”

Bailey said one new element of “BB3” is the “veto” in which the winner of a competition has the power to remove one of the two people nominated for eviction from the house – forcing the “head of household” to nominate a third person in his/her place.

“Personally, I think everyone should always hold on to the veto. If they give it up, then they create enemies,” she said.

Bailey thinks she knows who’s going to win “BB3.” “It will not be a woman, because eventually the guys are going to pluck [the women] off one by one,” she said “The winner will not be Amy, Chiara, Lisa or Danielle.”